Someone viewed my property online and decided he wanted to rent it. I mailed him the lease and he signed it and mailed it back along with the full rent for the entire lease. He then came to move in and asked that I changed the carpet and so I changed the carpet. He took the keys and started moving in his things. He contacted me the following day to say he changed his mind and gave me back the keys. He then asked for his money back. What are my rights as a landlord? What should I do?